Effects of Er 2 O 3 on Electrical Properties of the SnO 2 .CoO.Ta 2 O 5 Varistor System

We investigate the effects of Er2O3 on electrical properties of the SnO2.CoO.Ta2O5 varistor system sintered at 1400 degrees C. It is found that all the samples have excellent nonlinear electrical characteristics and the sample with 0.50 mol% Er2O3 has the best nonlinear electrical property and the highest nonlinear coefficient (α = 43.7). The high nonlinear coefficient value obtained in the system indicates that the SnO2-based varistor is a candidate for ZnO-based varistors in commercial applications. Er2O3 additive can significantly affect the average grain size. With increasing Er2O3 concentration from 0.10 mol% to 1.00 mol%, the average grain size decreases from 21.2 μm to 10.6 μm, the breakdown electrical field increases from 208 V/mm to 459 V/mm, and the relative electrical permittivity decreases from 2440 to 1210. The reason that the grain size decreases with increasing Er2O3 concentration is explained. Also, we present a modified defect barrier model to illustrate the grain-boundary barrier formation of Er2O3-doped SnO2 based varistors.